Activation and inactivation of taurine efflux in hyposmotic and isosmotic swelling in cortical astrocytes: Role of ionic strength and cell volume decrease
✍ Scribed by V. Cardin; C. Peña-Segura; H. Pasantes-Morales
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 103 KB
- Volume
- 56
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
A decrease in intracellular ionic strength appears involved in the activation of swelling-elicited 3 Htaurine efflux in cortical cultured astrocytes. Hyposmotic (50%) or isosmotic urea-induced swelling leading to a decrease of intracellular ionic strength, activated 3 H-taurine efflux from a rate constant of about 0.008 min -1 to 0.33 min -1 (hyposmotic) and 0.59 min -1 (urea). This efflux rate was markedly lower (maximal 0.03 min -1 ) in isosmotic swelling caused by K ؉ accumulation, where there is no decrease in ionic strength, or in cold (10°C) hyposmotic medium (maximal 0.18 min -1 ), where swelling is reduced and consequently intracellular ionic strength is less affected. Also, astrocytes pretreated with hyperosmotic medium, which recover cell volume by ion accumulation, did not release 3 H-taurine when they swelled by switching to isosmotic medium, but when volume was recovered by accumulation of urea, taurine release was restored. These results point to a key role of ionic strength in the activation of osmosensitive 3 H-taurine efflux. In contrast, its inactivation was independent of the change in ionic strength but appears related to the reduction in cell volume after swelling, since despite the extent or direction of the change in ionic strength, the 3 H-taurine efflux did not inactivate in isosmotic KCl-elicited swelling when cell volume did not recover nor in hyposmotic swelling when RVD was impaired by replacing NaCl in the medium by permeant osmolytes. J.